Remove the "halves" cover style again

Tried in macOS Terminal: it does not look good there either.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019reK4DUGYqDUjniWYJvwUW

internal/ui/settings.go

@@ -26,7 +26,7 @@ type settingsValues struct {
 	notify, bell                                      bool
 }
 
-var coverStyles = []string{"auto", "kitty", "sextant", "quadrant", "halves", "cells"}
+var coverStyles = []string{"auto", "kitty", "sextant", "quadrant", "cells"}
 
 // settingsFrom reads the settings in use.
 func settingsFrom(c *config.Config) settingsValues {